This application claims priority from Japanese Patent Application No. 2002-039247 filed Feb. 15, 2002, which is incorporated hereinto by reference.
1. Field of the Invention
The invention relates to a liquid jet print head and a liquid jet printing apparatus with the same.
2. Description of the Related Art
Liquid jet printing apparatuses with liquid jet print heads are well known. In such a liquid jet printing apparatus, print liquid (ink) is supplied to the liquid jet print head having printing devices such as electrothermal converting elements and piezoelectric elements, and electric pulse signals corresponding to image data are sent to the printing devices. Then, the liquid jet print head ejects print liquid to print desired images on a print medium. As has been described, so called non-impact type liquid jet printing apparatuses can print images on various print media at high speed with low noise. Thus, they are widely adopted as printers, word processors, facsimile, copiers and mailing machines.
FIGS. 20 and 21 show a conventional print head for the liquid jet printing apparatus. The liquid jet print head 100 shown in these drawings has a plurality of electrothermal converting elements (not shown) serving as printing devices. The print head prints images on a print medium by ejecting ink drops from micro nozzles corresponding to each of electrothermal converting elements. Electrothermal converting elements (heaters) for generating heat are arranged on a printing device substrate 101. Also, and a plurality of nozzles 101a corresponding to the electrothermal converting elements are arranged on the printing device substrate 101. As shown in FIG. 21, the printing device substrate 101 is bonded to a supporting substrate 102 made of aluminum, ceramics and the like.
On the supporting substrate 102, wiring sheets 103 such as TAB and FPC are bonded so as to supply electric signals to the printing device substrates 101. Each printing device substrate 101 is electrically connected with the wiring sheet 103 by wire bonding or lead bonding. The wiring sheets 103 are connected to a contact substrate 105 such as PWB, TAB and FPC having a plurality of contact pads 104 for electric connection with the liquid jet printing apparatus (not shown). The printing device substrates 101 and contact substrate 105 are connected with a flow path forming member 106 having flow paths 106a for print liquid.
A liquid jet print head shown in FIGS. 22 and 23 is also well known The liquid jet print head 200 of these drawings includes a printing unit 201 (FIG. 22) for producing ink drops and a print liquid storage unit 220 (FIG. 23) for supplying print liquid to the printing unit 201. The printing unit 201 includes a printing device substrate 203 where a plurality of printing devices (electrothermal converting elements) 202 that generate energy for ejecting ink drops are arranged. The printing device substrate 203 is bonded to a supporting substrate 204 made of aluminum, ceramics and the like.
Further, a wiring substrate 205 that provides an electric connection with the liquid jet printing apparatus is mounted on the supporting substrate 204 in addition to the printing device substrate 203. The printing device substrate 203 and the wiring substrate 205 are electrically connected with each other by wire bonding or lead bonding. On the printing device substrate 203, shift registers for driving and wiring patterns are formed in addition to the printing devices 202, and they are all formed together with the printing devices 202 on the printing device substrate 203 by silicon device techniques. Contact pads (not shown) are formed on the wiring substrate 205 for electric coupling with the liquid jet printing apparatus.
On the top surface of the printing device substrate 203, a ceiling plate 207 having concave portions is bonded by a pressing means such as a plate spring 206 or with an adhesive. As a result, a liquid chamber 208 and liquid flow paths 209 are formed between the printing device substrate 203 and the ceiling plate 207. An orifice plate 210 is aligned and bonded to the end faces of the printing device substrate 203 and the ceiling plate 207. As shown in FIG. 22, the orifice plate 210 has a number of micro nozzles 210a for ejecting ink drops in positions corresponding to the each of printing devices 202 on the printing device substrate 203.
A flow path forming member 212 has a flow path for print liquid and is fixed to the supporting substrate 204. The flow path of the member 212 communicates with an inlet 207a formed on the top of the ceiling plate 207. Through the inlet, print liquid is supplied to the liquid chamber 208 formed between the printing device substrate 203 and the ceiling plate 207. The flow path forming member 212 has a porous member 214 faced with the contact area with the ceiling plate 207, and the porous member 214 traps impurities contained in print liquid.
On the other hand, as shown in FIG. 23, the print liquid storage unit 220 includes a frame 221 having a liquid chamber (not shown) for storing print liquid therein. The frame 221 serves as a casing that holds the printing unit 201. The printing unit 201 is fixed to the frame 221 with screws 222 or an adhesive. Their contact portion is sealed with a predetermined sealing agent to be airtight. In the liquid jet print head 200, the print liquid stored in the liquid chamber of the frame 221 is sent to the printing device substrate 203 via the flow path forming member 212 and the ceiling plate 207.
As seen from FIGS. 20 and 21, the liquid jet print head 100 has a structure where a plurality of printing device substrates 101 are bonded to a single supporting substrate 102. On the other hand, as seen from FIGS. 22 and 23, the liquid jet print head 200 has a structure where a single-piece printing device substrate 203 is bonded to the supporting substrate 204. That is, some liquid jet print heads have a structure where a single-piece printing device substrate is bonded to the supporting substrate, and others have a structure where a plurality of printing device substrates are bonded to the supporting substrate. Some of the liquid jet printing apparatuses using the liquid jet print head having only a single-piece printing device substrate have a single liquid jet print head, and others have more than one liquid jet print head.
When the electrothermal converting element receives an electric pulse signal serving as a print signal, the electrothermal converting element provides thermal energy with print liquid. Then, the liquid jet print head utilizes the pressure of bubbles formed by film boiling in print liquid caused by the thermal energy so as to eject ink drops. Some of the liquid jet print heads using electrothermal converting elements eject print liquid in the direction parallel to the substrate where the electrothermal converting elements are arranged (so called, edge shooters, see FIG. 22), and others eject print liquid in the direction perpendicular to the substrate where the electrothermal converting elements are arranged (so called, side shooters).
If a printing device substrate in such a liquid jet print head is excessively heated during operation, there may be problems to the electric pulse signals and to the bubbling state of print liquid. Thus, some heat-dissipating mechanisms are usually provided with the liquid jet print head. For example, in the edge-shooter type liquid jet print head, the supporting substrate disposed on the backside of the silicon printing device substrate is made of aluminum, aluminum alloys or ceramics so that it serves as a heat-dissipating member.
On the other hand, in the side-shooter type liquid jet print head, such a simple method is known that dissipates heat by using print liquid itself ejected from the print liquid storage unit via the back side of the printing device substrate. In side-shooter type liquid jet print heads where high density printing devices may produce much heat, the supporting substrate is formed so as to serve as a heat-dissipating member having a large contact area, and the printing device substrate is fixed to this supporting substrate.
In such liquid jet print heads where nozzles (ink nozzles) are densely arranged and that eject print liquid using a pressure change produced by thermal energy, there will be a phenomenon (called the cross-talk) where the ejection of ink drops becomes unstable because of a pressure wave and heat diffusion from neighboring ink nozzles. To prevent the cross-talk by prohibiting simultaneous ink ejection from neighboring nozzles, the ink nozzles are divided into two or more groups, and the electric pulse signals are controlled so that the each of nozzle groups eject print liquid one after another. For high speed printing, the liquid jet print head must be driven with a high frequency. In such a case, the ink nozzles may be arranged with some displacements corresponding to delay time in accordance with ejection sequence, so as to control ink ejection from each nozzle group and prevent unfavorable dot patterns.
When the amount of tilting of the ink nozzles are different between nozzle groups, the quality of printed images degrades if the print head is tilted too much with respect to the carriage, or if the printing device substrate is positioned with insufficient accuracy and the direction of each nozzle is displaced from the predetermined one. For example, in a liquid jet printing apparatus with a plurality of liquid jet print heads for full-color printing, if one print head is installed in a tilted state with respected the other heads, the dots from the tilted head overlap those from other heads, and the quality of printed images may degrade seriously. Similarly, when a single print head is used for printing, if the print head is tilted beyond a limit, the image quality may also degrade seriously. In particular, in the case of a serial type liquid jet printing apparatus using an elongated print head, the mismatch in boundaries between scanning regions becomes conspicuous.
For these reasons, the amount of tilting of nozzles (nozzle array) in the print head with respect to the printing apparatus (carriage) must be as close as possible to a predetermined level when the print head is installed in a liquid jet printing apparatus. To achieve this, projections are provided with the frame serving as the casing of the liquid jet print head. The liquid jet print head is positioned in the printing apparatus by engaging the projections with predetermined positions of the carriage. However, since the casing of the print head, which usually has a complex shape, is typically made of resin, the projection may deform because of insufficient rigidity. Deformation of the projection may deteriorate the positioning accuracy of the liquid jet print head and the positioning repeatability at installing and replacing the print head.
Accuracy in the amount of tilting of the nozzles of the print head with respect to the printing apparatus (carriage) is determined by the positioning accuracy of the printing device substrate (or a orifice plate) including nozzles as well as the installing accuracy of the liquid jet print head in the predetermined position of the carriage. Thus, in order to solve the above problems associated with the quality of printed images, it is very important to improve the positioning accuracy of the nozzles (array of nozzles) in the liquid jet print head, that is, the installing accuracy of the printing device substrate or the orifice plate in the predetermined positions of the print head.
However, as described above, it is difficult to prevent the increase of positioning errors because a number of components including the member having nozzles, the casing and the like are assembled to complete a liquid jet print head. For example, in a liquid jet print head where a plurality of printing device substrates are installed, each of printing device substrates must be fixed to the supporting substrate with high accuracy using semiconductor mounting techniques. In addition, even in a liquid jet print head using a single printing device substrate, expensive materials are required for the print head and the carriage, and machining of high accuracy is required. If strictly controlling the dimensional accuracy of the liquid jet print head and the carriage and the installing accuracy of the print head on the carriage for maintaining the quality of printed images, the manufacturing yield of the print heads and apparatuses may decrease and thus their manufacturing efficiency may decrease. At the same time, the costs of the liquid jet print head and apparatus may increase.
The present invention provides a liquid jet print head and a liquid jet printing apparatus capable of easily improving various accuracies required to maintain the quality of printed images high, improving productivity and reducing cost.
A liquid jet print head of the invention comprises a printing unit including: a printing device array having a plurality of nozzles for ejecting print liquid and a plurality of printing devices; and a supporting member, to which the printing device array is attached, having a print liquid flow path for supplying print liquid to the printing device array, the printing unit adapted to be capable of sending electric signals for printing to the printing device array; and a print liquid storage unit connectable to the printing unit, the print liquid storage unit storing print liquid for the printing unit, wherein the supporting member is formed to define a reference plane for determining the amount of tilting of an array of the nozzles with respect to the supporting member when the printing device array is aligned and fixed to a predetermined position of the supporting member, and wherein the reference plane can be used as a reference for positioning when the print head is installed in the liquid jet printing apparatus.
Another liquid jet print head of the invention comprises a printing unit including a first-direction reference portion, a second-direction reference portion and a third-direction reference portion, which can be used as three-dimensional positioning references when the print head is installed in the liquid jet printing apparatus. In this print head, a reference for positioning to align and fix the printing device array in a predetermined position of the supporting member is used as at least one of the first-direction reference portion, the second-direction reference portion and the third-direction reference portion.
Another liquid jet print head of the invention comprises a printing device substrate having an array of a plurality of nozzles for ejecting print liquid and a plurality of printing devices arranged in correspondence with the plurality of nozzles; and a supporting member for supporting the printing device substrate and having a print liquid flow path for supplying print liquid to the nozzles, wherein the supporting member includes a plurality of projections arranged along the array of nozzles, the projection capable of being in contact with a predetermined position of the liquid jet printing apparatus when the print head is installed in the liquid jet printing apparatus.
The liquid jet printing apparatus of the invention comprises one of the above liquid jet print heads.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.